Index: trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFSheet.java
===================================================================
--- trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFSheet.java	(revision 1783971)
+++ trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFSheet.java	(working copy)
@@ -70,14 +70,23 @@
     private int outlineLevelRow = 0;
     private int lastFlushedRowNumber = -1;
     private boolean allFlushed = false;
+    private SXSSFRow firstRowsArray[] = null;
 
     public SXSSFSheet(SXSSFWorkbook workbook, XSSFSheet xSheet) throws IOException {
         _workbook = workbook;
         _sh = xSheet;
         _writer = workbook.createSheetDataWriter();
         setRandomAccessWindowSize(_workbook.getRandomAccessWindowSize());
+        setRandomAccessAtTop(_workbook.getRandomAccessAtTop());
         _autoSizeColumnTracker = new AutoSizeColumnTracker(this);
     }
+    
+	private void setRandomAccessAtTop(int randomAccessAtTop) {
+		if (randomAccessAtTop > 0) {
+			firstRowsArray = new SXSSFRow[randomAccessAtTop];
+			for (int i = 0; i < firstRowsArray.length; i++) firstRowsArray[i] = null;
+		}
+	}
 
     /**
      * for testing purposes only
@@ -185,7 +194,10 @@
     @Override
     public SXSSFRow getRow(int rownum)
     {
-        return _rows.get(rownum);
+    	if (firstRowsArray != null && rownum < firstRowsArray.length && firstRowsArray[rownum] != null)
+    		return firstRowsArray[rownum];
+    	else
+    		return _rows.get(rownum);
     }
 
     /**
@@ -1901,6 +1913,7 @@
         if (firstRowNum!=null) {
             int rowIndex = firstRowNum.intValue();
             SXSSFRow row = _rows.get(firstRowNum);
+            if (firstRowsArray != null && rowIndex < firstRowsArray.length) firstRowsArray[rowIndex] = row;
             // Update the best fit column widths for auto-sizing just before the rows are flushed
             _autoSizeColumnTracker.updateColumnWidths(row);
             _writer.writeRow(rowIndex, row);
Index: trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java
===================================================================
--- trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java	(revision 1783971)
+++ trunk/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java	(working copy)
@@ -103,7 +103,8 @@
     private final Map<XSSFSheet,SXSSFSheet> _xFromSxHash = new HashMap<XSSFSheet,SXSSFSheet>();
 
     private int _randomAccessWindowSize = DEFAULT_WINDOW_SIZE;
-
+    private int _randomAccessAtTop = 0;
+    
     /**
      * whether temp files should be compressed.
      */
@@ -272,6 +273,34 @@
     }
 
     /**
+     * Construct an empty workbook and specify the window for row access.
+     * First rows will be held in memory for later reference, for example to construct pivot table.
+     * <p>
+     * When a new node is created via {@link SXSSFSheet#createRow} and the total number
+     * of unflushed records would exceed the specified value, then the
+     * row with the lowest index value is flushed and cannot be accessed
+     * via {@link SXSSFSheet#getRow} anymore.
+     * First rows are kept in memory according to rowAccessFixedTop parameter.
+     * </p>
+     * <p>
+     * A value of <code>-1</code> indicates unlimited access. In this case all
+     * records that have not been flushed by a call to <code>flush()</code> are available
+     * for random access.
+     * </p>
+     * <p>
+     * A value of <code>0</code> is not allowed because it would flush any newly created row
+     * without having a chance to specify any cells.
+     * </p>
+     *
+     * @param rowAccessWindowSize the number of rows that are kept in memory until flushed out, see above.
+     * @param rowAccessFixedTop the number of first rows that are kept in memory permanently.
+     */
+    public SXSSFWorkbook(int rowAccessWindowSize, int rowAccessFixedTop){
+    	this(null /*workbook*/, rowAccessWindowSize);
+    	setRandomAccessAtTop(rowAccessFixedTop);
+    }
+    
+    /**
      * See the constructors for a more detailed description of the sliding window of rows.
      *
      * @return The number of rows that are kept in memory at once before flushing them out.
@@ -507,6 +536,14 @@
         return _wb;
     }
 
+	public int getRandomAccessAtTop() {
+		return _randomAccessAtTop;
+	}
+
+	private void setRandomAccessAtTop(int _randomAccessAtTop) {
+		this._randomAccessAtTop = _randomAccessAtTop;
+	}
+    
 //start of interface implementation
 
     /**
@@ -1363,6 +1400,6 @@
     public int addOlePackage(byte[] oleData, String label, String fileName, String command) throws IOException {
         return _wb.addOlePackage(oleData, label, fileName, command);
     }
-    
+        
 //end of interface implementation
 }